1. Field of the Invention
The invention relates to the field of apparatus and methods for using LEDs or other light sources to generate predetermined offset wide profile two dimensional illumination patterns on a surface using a light source which has been optically modified to provide a corresponding wide profile beam or an array of multiple modified light sources.
2. Description of the Prior Art
Light emitting diodes (LEDs) are now being utilized for general lighting applications such as street lights, parking garage lighting, parking lots and many interior applications as well. LEDs have reached efficiency values per watt that outpace almost all traditional light sources, such as HID, compact fluorescent, incandescent, etc. However they are still very expensive in lumens per dollar compared to these traditional lamp sources. Therefore, optical, electronic and thermal efficiencies remain very important disciplines to realize products that are cost competitive with traditional lighting means. What is needed is an LED lighting solution with competitive or superior optical efficiency and hence increased energy efficiency as compared to these traditional lighting systems.
The initial investment cost of LED illumination is expensive when compared with traditional lighting means using cost per lumen as the metric. While this may change over time, this high cost places a premium on collection and distribution efficiency of the LED optical system. The more efficient the system, the better the cost-benefit comparison with traditional illumination means, such as incandescent, fluorescent and neon.
A traditional solution for generating broad beams with LEDs is to use one or more reflectors and/or lenses to collect and then spread the LED energy to a desired beam shape and to provide an angled array of such LEDs mounted on an apparatus that has the LEDs and optics pointing in various planes or angles. Street light illumination patterns conventionally are defined into five categories, Types I-V.
Another technique is to use a collimating lens and/or reflector and a sheet optic such as manufactured by Physical Devices Corporation to spread the energy into a desired beam. A reflector has a predetermined surface loss based on the metalizing technique utilized. Lenses which are not coated with anti-reflective coatings also have surface losses associated with them. The sheet material from Physical Devices Corporation has about an 8% loss.
Total internal reflectors (TIR) lenses, such as TIR 44 illustrated in FIG. 13, have been previously used to combine refracted light (e.g., ray 52 through crown 56 in FIG. 13) with totally internally reflected light (e.g., ray 50 reflected from surface 46 in FIG. 13). Some of the rays with TIR lens 44 are reflected from surface 46 and often several other internal surfaces in multiple reflections in TIR lens 44 to be directed across centerline 54 of TIR lens 44. However, only a portion of surface 46 is positioned at the correct angle with respect to the incident light from light source 1 to be totally reflected with the balance of the incident rays being refracted through surface 46 and sent in directions other than the desired beam direction through crown 56. Furthermore, even in the case of those rays which are nominally “totally internally reflected” from surface 46, the internal reflection, in actuality, is not total due to imperfections in the optical surface 46 and optical material out of which lens 44 is made so that a portion of these TIR rays are actually refracted through surface 46, such as depicted by ray 48. Moreover, any rays which are reflected by surface 46 must first be refracted by inner surface 58 of TIR lens 44, thereby further decreasing the fraction of light which ultimately reaches the intended beam since each refraction and reflection decreases the light intensity by as much as 8% depending on optical qualities and figure losses.
One example of prior art that comes close to a high efficiency system is the ‘Side-emitter’ device sold by Philips Lumileds Lighting Company. However, the ‘side-emitter’ is intended to create a beam with an almost 90 degree offset from the centerline of the radiation pattern of the LED in an intensity distribution that is azimuthally symmetric. It has internal losses of an estimated 15% and only provides azimuthally symmetric beam profiles, and not azimuthally asymmetric or azimuthally directed beams, i.e. the plots of the isocandela graph in three dimensions is a surface of revolution. Another Lumileds LED, commonly called a low dome, has a lens over the LED package to redirect the light, but it is to be noted that it has a singular distinct radius of curvature on the front surface and is not intended, nor is it suited for generating a smooth two dimensional patterned surface such as needed for illumination of a street or parking lot.
There are many systems designed that utilize armatures to hold optic 22 systems at angles to the ground to obtain spread beam patterns on the ground. Such armatures are often complex and/or difficult to assemble.
There are also several systems that slide the optics off center in one direction allowing the beam to move off center in the opposite direction of a centerline of the system in order to skew illumination patterns.
What is needed is a device that creates a wide angle beam, azimuthally asymmetric spread beam, that can be created with a method that allows the designer to achieve a smooth two dimensional surface at a distance: that can be an array of LEDs all mounted on or in the same plane, and which is not subject to the inherent disadvantages of the prior art.